What is a thunderstorm?

Thunderstorm is a local convective weather accompanied by lightning strike and lightning. It must be produced in strong cumulonimbus clouds, so it is often accompanied by strong showers or heavy rains, sometimes accompanied by hail and tornadoes, and belongs to a strong convective weather system. Cumulonimbus clouds that form thunderstorms develop vigorously, and there are often ice crystals on the upper part of the clouds. The attachment of ice crystals, the breaking of water droplets and air convection make clouds generate charges. The distribution of charge in the cloud is very complicated, but generally speaking, the upper part of the cloud is mainly positive charge, the middle and lower part of the cloud is mainly negative charge, and there is a small positive charge area in the strong updraft in front of the lower part of the cloud. Therefore, there is a potential difference between the top and bottom of the cloud. When the potential difference reaches a certain level, discharge will occur, which is the usual lightning phenomenon. In the process of discharge, the temperature in the flash path suddenly rises, which makes the air volume expand rapidly, thus generating shock waves and leading to strong lightning. When the clouds are very low, sometimes a discharge between clouds can be formed, which is lightning strike. Therefore, thunderstorm is the product of atmospheric instability, and it is the general name of cumulonimbus clouds and their accompanying disastrous weather. The duration of thunderstorms is generally short, and the life history of a single thunderstorm is generally less than 2 hours. There are more thunderstorms in the south of China than in the north, and there are more thunderstorms in the mountains than in the plains. Most of them appear in summer and autumn, and only occasionally in southern China in winter. Thunderstorms usually occur in the afternoon. At night, due to the radiation cooling of the cloud top, the temperature stratification in the cloud becomes unstable, and it can also cause thunderstorms, which are called night thunderstorms.

Thunderstorm is a discharge phenomenon in the atmosphere, usually accompanied by showers, and sometimes there are strong convective weather such as local strong winds and hail. Severe thunderstorm sometimes brings disasters, such as lightning endangering personal safety, direct damage to household appliances and computer rooms by lightning or induced lightning, and sometimes fires. Lightning is a discharge phenomenon in the atmosphere, which is produced in cumulonimbus clouds. During the formation of cumulonimbus clouds, some clouds are positively charged and some clouds are negatively charged. Their electrostatic induction to the earth makes the ground or the surface of buildings (structures) produce different charges. When the charge accumulates to a certain extent, the electric field intensity between different charge clouds or between clouds and the earth can break through the air (generally 25-30KV/cm) and start to discharge freely, which is called "pilot discharge". Cloud-to-ground pilot discharge is the gradual development of cloud jumping to the ground. When it reaches the ground (buildings on the ground, overhead transmission lines, etc.). ), it will produce a reverse pilot main discharge from the ground to the cloud. In the main discharge stage, due to the strong neutralization of opposite charges, a large lightning current (usually several hundred thousand amperes to several hundred thousand amperes) will be generated, followed by strong lightning and loud noise, forming lightning.

[Edit this paragraph] Types of thunderstorms

Thunderstorms can be divided into three types, namely single thunderstorm, multi-cell thunderstorm and super-cell thunderstorm. The way to distinguish them depends on the instability of the atmosphere and the relative wind speed at different levels (see wind shear).

When the atmosphere is unstable, but there is little or no wind shear, a single cell storm will occur. These thunderstorms are usually short-lived and will not exceed 1 hour. There are many opportunities to see this kind of thunderstorm on weekdays, so it is also called thunderstorm.

Multi-cell storm is composed of multiple single thunderstorms, which is the further development of single thunderstorms. At this time, due to the flow of air, a gust zone will be formed. This gust zone can extend for miles. If the wind speed increases, the air pressure increases and the temperature drops, the gust area will become larger and larger, and it will attack a larger area.

Supercell storm occurs when the wind shear is extremely high, and it is composed of various thunderstorms. This kind of thunderstorm is the most destructive, and there is a 30% chance of a tornado.

According to the different atmospheric and topographic conditions when thunderstorms are formed, thunderstorms are generally divided into three types: thermal thunderstorms, frontal thunderstorms and topographic thunderstorms. In addition, some people classify winter thunderstorms as one category, which is called winter thunderstorms. In the south of China, so-called dry sky thunder, also known as dry thunderstorm, often occurs.

[Edit this paragraph] for lightning strike

Lightning strike refers to the rapid discharge between one part of charged cloud and another part of charged cloud, or between charged cloud and the earth. The latter, that is, the emission of clouds to the earth, is extremely harmful to buildings, people and electronic equipment in buildings, and is the main object of human research.

[Edit this paragraph] Thunderstorm Generation

3 ~ 5 pieces of lightning discharge at the same time at a very close distance, which is called thunderstorm. Thunderstorms sometimes produce fireballs with diameters ranging from15cm to 2m. Some of them are very large, exceeding 5m, but they usually occur in minefields. After a thunderstorm produces a fireball, it often attacks living things and releases powerful energy. The fireball produced by a thunderstorm travels at an ultra-high speed of several meters per second to dozens of meters per second. It depends on the size of the fireball. The fireball formed by thunderstorm in minefield is much faster than the speed of human running, regardless of its size. Therefore, the way to avoid a thunderstorm in a minefield is to stay still and make no sound. The moving time is longer than that in a place without a minefield, usually about 2-6 hours, and of course the running time is longer. More importantly, some fireballs will open doors and attack people, while others will attack houses. This is different.

[Edit this paragraph] The causes of Lei Yun

The cause of Lei Yun, or the energy contained in it, mainly comes from the movement of the atmosphere. The movement of airflow, friction and the action of wind on clouds make them cut the magnetic lines of the earth's magnetic field, further separating and polarizing different charges and charged particles, and finally forming a Lei Yun with a large amount of charges. When the electric field intensity in Lei Yun is large enough, it will cause internal discharge in Lei Yun, or strong discharge between Lei Yun, or discharge between the earth and other objects in Lei Yun, which is called lightning.

[Edit this paragraph] How to evaluate the intensity of lightning activity in a certain area?

It is customary to use "thunderstorm days", that is, how many days in a year thunder occurs in this area, and thunder can be heard in the ear to indicate the intensity of lightning activity in this area.

Average annual thunderstorm days in this area

Hainan Island and Guangdong Leizhou Peninsula 100 days or more.

More than 80 days south of 23℃ north latitude.

South of the Yangtze River > 40 days

Most areas north of the Yangtze River 15~40 days

Northwest China < 15 days

[Edit this paragraph] Matters needing attention in thunderstorm weather

Stay indoors. People who work outdoors should hide in buildings.

Do not swim or do other water sports. Get out of the water and find a place to hide.

Avoid using phones with plugs or other electrical appliances, including computers.

Do not touch antennas, faucets, water pipes, barbed wire or other similar metal equipment.

Avoid taking a shower with a shower.

Do not handle flammable items in open containers.

Don't stand on the top of the mountain or near objects with high conductivity. Trees or masts are easily struck by lightning and should be kept as far away as possible. After lightning strikes an object, the current will spread through the ground, so don't lie on the ground. Wet ground is especially dangerous. You should squat down to minimize the contact area with the ground.

Hikers and other outdoor activities should carry radios with them and pay attention to the latest weather news of the Observatory.

Always pay attention to the possibility of heavy rain, and don't stay in rivers, streams or low-lying places.

Motorists should be careful of strong winds when passing through expressway or flyovers.

Small boats at sea should be careful of strong winds or waterspouts.

If you encounter a tornado, you should immediately hide in a solid building. Stay away from the window, squat on the ground, and protect your head with your hands or thick pads. If you are outdoors, stay away from trees, cars or other objects that may be blown up by tornadoes.